Rubber derivatives



Patented pr. Y278, 1936 UNITED STATES 2,039,191' PATENT oFFlcE ducersResearch Association, London, England, a body corporate of Great BritainApplieatien January 14, 1935, serialy No. 1,784 In Great Britain May2,4,- 1933 claim. (c1. 18-55) This invention relates to, .;rubberderivatives and more especially to the treatment4 of chlorinated rubberwhereby industrially useful products may be obtained.

One process of treatment according to the invention consists insubjectingY chlorinated rubber to elevated pressure andv temperature andin releasing the pressure while the temperature is maintainedor beforeappreciable lowering of the temperature has taken place, instead ofallowing thematerial to cool under pressure, whereby there is the mostsurprising result that a tough brous product of low specic gravity isobtained.

In carrying out this treatment resort may be had to the apparatuscustomarily used for pressure moulding, the chlorinated rubber, usuallyin the form of a powder, being placed in the mould and heated toatemperature in the neighbourhood of S-3 5() F., .while beingsubjected tothe moulding pressure in the usualmanner, the pressure being thenreleased, e. g; by opening the mould. When cooled to normal temperaturea nbrous mass of low specic gravity. obtained which is water resistantand nonflarmnable.

-YIn the practice of the invention applied to the treatment of onesample the vchlorinated rubber in vpowdered form, a mass orthepowde'ris, for example, inserted in a pressure mould approximately 21AH indiameter and'subjected to a pressure suicient to keep the mould closed,while being heated to 325 F. for three minutes, the pressure thenbeingdreleased and the mass withinv the mould swelling up and beingrpermitted to cool under normal pressure conditions, whereupon a tough,water-resistant brous mass of non-communicating cells isl Aobtained'which has a specic gravity far less than the products normally obtainedfrom t he chlorinated rubber; indeed, the apparent specific gravity ofthe expanded material may be as low as 0.1 or even lower, which isobviously much less than that of the original chlorinated rubber, thespecific gravity or which is well known to be in the neighborhood of1.56.

Thisis. obvious in view of the fact that as the product is an expandedone it must necessarily have less than the speciic gravity of theoriginal substance from which the new product is formed.

It has also been found that the tough fibrous mass can be obtained by amodification of the process on the specialtype of press adapted forinjection moulding,` i. e`. the chlorinated rubber is,Y introduced intethe heated cylinder of the press, and without closing'. the injectionorifice, pressure is applied bymcans of the ram. The compressed andheated' material is extruded through the orice and immediately assumessome brous condition. With the chlorinated rubbers satisfactory resultsare readily obtained,

but with others difficulty is likely to be experienced in effecting theexpansion` of the mass when the pressureisreleased and the presentinvention also. comprehends developments, of the process rendering itmorereadily effective with chlorinated rubbers in general. v Witnthisobject in View, liquids which exert a considerable vapour pressure atlow tempera-v tures may be incorporated with the chlorinated rubberprior to,y the treatment at elevated pressure andv temperature, wherebyon the, pressureV being released expansion` readily takes place and atough fibrous product of low specic gravity is obtained.

Preferably the liquids incorporated withthe chlorinated rubber ar ethose organic liquids which are volatile under the temperatureconditions prevailing during the treatment, and it appears to beimmaterial whether such..liquids have a' solvent action .or .,not,benzene being .a typical solvent of chlorinated rubber capableof`producingv the desired result, which ,may also be obtained with alcohol,a typical noti- Solvent Waten lwhile volatile at the temperature .oftreatment, does not produce-.asaltisfactory expandefdlproduct andsimilarly sodium bicarbonate is ineffective.

. Applying the treatment involving unev uquid addition, with each 30gms. of the chlorinated rubber about 5 c. c. of benzene or alcohol iswell mixed ina mortar before beingY placedy in. .the mould 4and heatedto a temperature of .between 320'? to 350 F., while being subjectedtothe moulding pressure inthe usual manner. .A .On releaseof thepressure. the material expands and a bro'us mass of low specic gravityis obtained which is water resistant` and non-lammable.V

The treatment may becarried out as a con, tinuous process, resort beinghad to the type of press employed for .the extrusion of thermoplasticmaterials such as those derived from casein and celluloseacetataand theinvention will now be described with. reference -to Ythe accompanyingdrawingy which illustrates diagrammatically two forms of apparatus whichmay be employed for .obtaining the expanded product, and in whichdrawing- Fig. 1 is a viewof a simplied form of mould for heating andcompressing chlorinated rubber, while Fig. 2 shows apparatus bywhichtheexpanded fibre may be extruded continuously in sheet form.

Referring now to the drawingv first, more, particularly v to Fig. 1,the` heated platens of a.

hydraulic press are indicated at l and 2.the

mouldatf 43and a.cov er for suchmouldat 4,'

this latterf VbeingA inthe form of a plunger by means of which pressuremay be applied to the contents of the mould by closing the press.

The empty mould 3 is heated for about fortyfive minutes at 350 F. and isthen lled with chlorinated rubber indicated at 5. Just sufficientpressure is applied by the plunger 4 to keep the mould closed, and it isallowed to stand under heat and pressure for about five to thirtyminutes according to the size of the mould. The mould 3 is furnishedwith an aperture or slit 8 and during this period the aperture is closedin any appropriate manner.

The aperture or slit 6 is then opened and the material slowly extrudedby depressing the plunger 4, the extruded product expanding whenreleased to atmospheric pressure, as shown at 'I, and giving theexpanded product of low specific gravity which is water resistant andnon-flammable.

Referring now to Fig. 2 where apparatus for carrying out the processcontinuously and giving a product of sheet form is illustrateddiagrammatically, I I indicates a cylindrical press to which thechlorinated rubber is fed through a hopper I2, I3 being a feed screwrotated in any appropriate manner so as to feed the chlorinated rubberforwardly along the press towards the nozzle I4.

The body of the press I I is shown channelled or jacketed at I5 and ismaintained at the desired temperature by means of superheated steampassed through the channels, while the nozzle is maintained at aslightly higher temperature,

l for instance by means of gas jets or of an electrical resistance orresistances (not shown), the temperatures being controlledthermostatically, if desired.

I6 and I'I indicate pairs of rollers through which the expanded materialis passed on extrusion, the first pair of rollers I6 being convenientlyheated, whereby too rapid cooling of the product is prevented.

The screw conveyor is rotated at a speed which will generate sufficientpressure in the forward end of the press to plasticize the chlorinatedrubber and cause it to extrude through the nozzle I4, whereupon itexpands to give the fibrous cellular product aforementioned which bypassage between the rollers is formed into a substantially at sheet.

The extrusion aperture in the nozzle preferably takes the form of anelongated slot giving the desired width of expanded material, while tofacilitate setting of the product the rollers II or additional rollersmay be artificially cooled.

As aforementioned, volatile liquids, such as benzene, toluene, xylene oralcohol, may be added to the chlorinated rubber before its introductioninto the press, and for some purpose also plasticizers such as triacetinor dibutyl phthalate may be incorporated to ensure, with a View interalia, the production of a stronger and tougher scribed. The chlorinecontent of the altered product is not widely divergent from that of thechlorinated rubber, one, for example, with a chlorine content ofapproximately 68.8 giving an expanded product with a chlorine content of67.6.

The solubility characteristics of the brous product are also similar tothose of the chlorinated rubber, e. g., it is soluble in benzene, carbonbisulphide and trichlorethylene and practically insoluble in water,ethyl, alcohol and petroleum hydrocarbons.

In other respects, however, the expanded material possesses markedadvantages, for although it is remarkably light it is non-flammable,comparatively resistant to moisture and substantially odourless.Moreover, it is comparatively strong and resilient and should prove ofexceptional use as an insulating medium.

By the present invention stable and industrially valuable chlorinatedrubbers are obtained capable of a variety of uses.

What we claim is:-

1. A process for treating chlorinated rubber to obtain an expanded brousproduct consisting in the preliminary steps of adding tothe chlorinatedrubber organic liquids which exert a considerable vapour pressure at lowtemperatures to facilitate expansion of the product, and plasticizingagents to toughen the expanded product, and then subjecting it topressure and a temperature of between 320 to 350 F. and finallyreleasing the pressure before appreciable lowering of the temperaturehas taken place so that a tough expanded brous product results.

2. A fibrous expanded and water resistant product of chlorinated rubberhaving a network of non-communicating cells and a specicgravity as lowas .1 or less.

3. A process for treating chlorinated rubber to Obtain an expandedfibrous product consisting in subjecting it to pressure and an elevatedtemperature of between 320 and 350 F. and then releasing the pressurewhile the temperature is maintained or before appreciable lowering ofthe temperature has taken place, instead of allowing the material tocool under pressure.

4. A process for treating chlorinated rubber to obtain an expanded brousproduct, comprising the preliminary step of adding to the chlorinatedrubber an organic liquid, such as benzine or alcohol capable of exertinga considerable vapor pressure at low temperatures to facilitateexpansion of the material, then subjecting the resulting material topressure and a temperature between 320 and 350 F., and nally releasingthe pressure before appreciable lowering of the temperature has takenplace, instead of allowing the material to cool under pressure.

5. A process for treating chlorinated rubber to obtain an expandedfibrous product, comprising the preliminary step of adding to thechlorinated rubber a plasticizing agent, such as triacetin or dibutylphthalate, whereby a tougher expanded product is obtained, thensubjecting the resulting material to pressure and a temperature between320 and 350 F., and nally releasing the pressure before appreciablelowering of the temperature has taken place, instead of allowing thematerial to cool under pressure.

PHILIP SCHIDROWITZ. CYRIL AUBREY REDFARN.

